Chemical equipment pressure vessel damage causes

Chemical equipment pressure vessel belongs to special equipment, the destruction of more factors, but also in line with the principle of specific analysis of specific problems, to take effective measures to actively prevent fatal chemical equipment pressure vessel damage.
Chemical equipment pressure vessel operating environment is relatively complex, subject to corrosion and cracking and deformation and other causes of damage caused by quality problems, easy to cause fatal injury. Therefore, as opposed to the damage after the fact to deal with. More attention should be paid to prevention and control in advance to ensure the safe and stable operation of chemical equipment and pressure vessels, effectively extending the service life of the vessel. Due to the diverse forms and causes of damage to chemical equipment pressure vessels, the need to strengthen innovation in preventive measures and management tools to effectively play the role of chemical equipment pressure vessel management value.

1. Chemical equipment pressure vessel accident characteristics

Pressure vessels belong to the pressure equipment, refers to the greater danger and involves the safety of life pressure class special equipment and safety accessories, including pressure piping and boilers, etc.. Pressure vessels are of various types and can be classified according to the way they are pressurised, dividing them into internal and external pressure vessels. If the classification method is chosen for the pressure size, it can be divided into high pressure, low pressure and medium pressure and ultra-high pressure vessels. If the classification method chosen is the operating temperature, then it includes low temperature, high temperature and ambient temperature vessels. If it is classified according to the production method, it includes different classification methods such as forging, welding and casting containers, which are classified differently, but any chemical equipment pressure vessel in the process of use, can not ignore the control of its safety and reliability. Ltd. is specialized in the development of various types of automation control systems and automation projects in the chemical industry, the technical team has accumulated a wealth of technology and experience in the field of chemical automation control, is a focus on the development of chemical automation control systems, chemical automation projects and technical services of technology-based enterprises. The accident characteristics of chemical equipment pressure vessels are mainly reflected in the following aspects.

(1) High danger

Chemical products have high temperature and high pressure and toxicity and flammable and explosive characteristics, the possibility of fire and leakage and explosion of pressure vessels, in terms of risk is incomparable to other industries. The reactivity, toxicity and flammability of some chemical raw materials are the main reasons for the frequent occurrence of malicious accidents within chemical enterprises. When fires and explosions and leaks occur in chemical companies, they not only result in injuries and deaths, but also cause large economic losses.

(2) Environmental pollution

The raw materials and products used in chemical production, as well as intermediates and by-products, have a certain degree of industrial toxicity and corrosiveness. Leakage into water or air, especially untreated industrial substances, will not only cause varying degrees of environmental pollution, but also economic losses and casualties. Malignant accidents in chemical enterprises are generally characterised by the difficulty of management and the long duration of impact.

(3) Affecting the normal operation of equipment

Chemical enterprises have high requirements for the operation of industrial equipment, but most of the chemical equipment pressure vessel operating environment is harsh, long-term corrosion and high temperature and high pressure and other environments, by vibration and internal corrosive media and other factors, will make the equipment metal fatigue and other quality problems, will directly affect the normal operation of chemical equipment, which is also a chemical enterprise in the safe use of equipment management can not ignore the problem.

2. Chemical pressure vessel damage forms and causes and characteristics

(1) excessive plastic deformation

Once the pressure load of the chemical pressure vessel itself exceeds the already established value, it will lead to the pressure vessel wall of the chemical equipment gradually becoming thinner, or even in an unstable state. The vessel will also become deformed due to its excessive plasticity, or even lead to the direct rupture of the vessel, if the rupture is produced by excessive plasticity, the state of its fracture is a tearing effect, and the vessel will also be accompanied by a small amount of broken pieces, or not produce broken pieces. At the same time, the chemical equipment pressure vessel bursting energy, directly determine the size of the vessel burst mouth.

(2) excessive elastic deformation

The so-called elastic deformation, is when the chemical pressure vessel solid by the action of external forces, and then produced a certain deformation, this deformation is a direct form of expression, and when the external force is withdrawn, the object will gradually return to the original shape of the initial. For this reason, it can be referred to as an elastic property. This is a reversible deformation, usually, people will be called elastic deformation, but if in the use of chemical pressure vessels, there is excessive elastic deformation, easy to promote the chemical equipment pressure vessel in an unstable state, with the strengthening of the external force, chemical equipment pressure vessel will gradually to the degree of instability transition.

(3) large strain fatigue

Under the influence of alternating stress, the local structure of the discontinuity or openings around the receiver and other local areas of the chemical equipment pressure vessel, where the metal grains are subject to the greatest force, there will be slippage phenomenon, and then gradually to present tiny cracks. With the gradual increase and expansion of cracks at both ends, the chemical pressure equipment that is eventually formed is itself susceptible to fatigue and vulnerable to significant damage. The high pressure areas themselves are subject to very high stresses. Fatigue first appears in the local area facing the very high stresses, and the high stresses cause damage to the large strain areas. For this reason, it can also be called large strain fatigue, in the current analysis of chemical pressure equipment vessels in the use of the process found that it has the fatigue damage characteristics are mainly reflected in the following points, namely, container deformation is not obvious; rupture fracture mainly exists in the fatigue crack generated to the expansion area and the last fracture area of the two regions; chemical equipment pressure vessel failure due to cracking leakage; chemical equipment pressure vessel after repeated loading and unloading More likely to produce fatigue damage.

(4) Corrosion fatigue

The joint action, and then the formation of a new form of damage, if based on the material corrosion fatigue this angle of analysis, can be found that it will lead to the metal surface to occur extremely obvious local damage, resulting in fatigue cracking of the metal. Secondly, the protective film on the surface of the metal is damaged by the alternating tensile stress, resulting in surface corrosion. After the alternating stress has destroyed the protective film, the protective mould cannot be formed again, which will also lead to deposits in the corrosion pit, directly affecting the diffusion of oxygen, resulting in the protective film cannot be restored in a short period of time, which ultimately forms a vicious circle. However, the bottom of the corrosion pit, is always in a relatively active state of activity, easy to form the anode of the corrosion cell, and ultimately in the dual role of alternating stress and corrosion, the crack will continue to develop, until the final metal presents the phenomenon of fracture.

(5) Stress corrosion

In the analysis of stress corrosion, taking into account the stress corrosion is mainly refers to the tensile stress and metal corrosion medium joint action, and then the formation of a unique form of damage. When the chemical pressure vessel metal stress corrosion phenomenon, due to stress corrosion of two different factors, in a state of mutual promotion, where corrosion will directly reduce the effective cross-sectional area of the metal itself, and gradually form a gap in the surface of the metal, prompting its stress more concentrated. It is also necessary to take into account that the corrosion progress will be gradually accelerated based on the role of pre-stress, and the result is that the gap on the surface of the metal will become larger and larger, until the final fracture.

(6) Brittle rupture

Brittle rupture is not significant plastic deformation fracture, brittle rupture of the container parts often have fragments flying out, and present a broken piece; usually in low temperature conditions rupture accident; low and medium strength manufacturing of thick-walled containers and high strength steel pressure vessels, more likely to occur brittle fracture.

(7) Hydrogen corrosion rupture

As most of the industrial equipment, the pressure vessel in the production and use of the process are in the high temperature, high pressure situation. For this reason, the surface of the steel will adsorb a large number of hydrogen molecules. The hydrogen molecules will gradually decompose into hydrogen ions or atoms, leading to solid solution phenomena on the steel surface layer, and will even spread into the steel, and through hydrogen corrosion and hydrogen embrittlement and other forms, and constantly destroy the performance of steel. Starting from the analysis of hydrogen corrosion, hydrogen ions or atoms diffuse into the steel, will be combined into hydrogen molecules, partly with non-metallic inclusions or carbon and carbide chemical reaction, the generation of gas generation is not easy to dissolve. The products will gradually accumulate in the original tiny gaps in the grain boundaries, and then gradually form a local high pressure as well as force concentration, prompting the grain boundaries to gradually widen, and produce a certain amount of micro-cracking, and the mechanical properties of the steel is also gradually weakened at this stage.

(8) Creep

Metal containers in the external temperature and the role of stress under the influence of continuous change, after a long period of time caused by the accumulation of the wall is very vulnerable to breakage. Unlike plastic deformation, creep is influenced by temperature, which weakens the rigidity of the metal material. In addition, the resulting tensile stress will gradually weaken the performance and quality of the pressure vessel, thus contributing to the phenomenon of damage.

3. Pressure vessel damage analysis methods

Pressure vessels have a high chance of accidents, once a malignant event occurs, it will cause stoppage of production, corrosion effects, etc. belong to the direct cause of industrial equipment pressure vessel accidents, while the pressure vessel equipment governance chaos and technical file information is incomplete, the implementation of safety production responsibilities are not in place, safety production rectification and monitoring and inspection of elements such as insufficient, is the indirect cause of the vessel accident. In addition to the need to analyse through a simple investigation, it is also necessary to provide inspection of whether the vessel has a fracture, its rupture at the fracture and what kind of state, the physical and chemical properties of the vessel. To really find the cause of the accident, if necessary, can be carried out in the container destructive simulation tests, etc. In the technical inspection and accident investigation at the same time, the development of targeted treatment and preventive measures.
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